My invention relates to an apparatus for data transfer with interchangeable disklike record media such as flexible magnetic disks which may be packaged in cassette or cartridge form. More specifically, my invention deals with such an apparatus for use with a flexible magnetic disk or like data storage disk having a first opening defined centrally therein for receiving a drive spindle on a turntable included in the apparatus, and a second opening defined eccentrically therein for receiving a retractable drive pin arranged eccentrically on the turntable.
The above defined type of flexible magnetic disk and an associated data transfer apparatus or disk drive have both been suggested by Sony Corporation., of Tokyo, Japan, as disclosed in Japanese Laid Open Patent Application No. 57-36473, laid open to public inspection on Feb. 27, 1982, and in corresponding U.S. Pat. No. 4,445,155 issued Apr. 24, 1984. This known flexible magnetic disk has a diameter of 3.5 inches (86 millimeters) and is rotatably housed in a generally flat, boxlike envelope of relatively rigid plastics material to make up a disk cassette. Aside from its size, the magnetic disk differs from more conventional ones in having a center hub of magnetic material to be placed concentrically on a motor driven turntable included in the associated data transfer apparatus. The turntable has a permanent magnet mounted thereon for attracting the hub of the magnetic disk. Defined in the disk hub are a central hole for receiving the drive spindle projecting from the turntable, and an eccentric slot for receiving a retractable, spring energized drive pin arranged eccentrically on the turntable.
The drive spindle finds ready engagement in the center hole in the disk hub as the magnetic disk is loaded concentrically on the turntable. Except in very rare cases, however, the drive pin is out of register with the eccentric slot in the hub of the magnetic disk when the latter is placed on the turntable, and so does not become engaged therein unless the turntable is revolved relative to the disk. During such revolution of the turntable, the drive pin must be held retracted into the turntable as the disk hub is magnetically held in sliding contact with the turntable, and must enter the eccentric slot immediately upon register therewith. The drive pin is therefore mounted on a leaf spring on the underside of the turntable for longitudinal movement in a direction parallel to the axis of the turntable.
A problem heretofore encountered with this type of magnetic disk and data transfer apparatus for use therewith concerns the leaf spring supporting the drive pin. It is practically impossible to design the leaf sring so as to cause displacement of the drive pin only in its longitudinal direction. Consequently, when the magnetic disk is set into rotation, the drive pin in engagement therewith slants rearwardly with respect to the direction of the disk rotation. The degree of such slanting of the drive pin may differ from one model to another of the data transfer apparatus. I object to the variable, unpredictable degree of slanting of the drive pin as it makes impossible the determination of the exact angular position of the magnetic disk in rotation with the turntable.
In the data transfer apparatus for use with the magnetic disk cassette of the kind in question, the angular position of the disk on the turntable is not sensed from an index hole cut in the disk, as in the case of the disk cartridge disclosed in, for instance, Castrodale et al. U.S. Pat. No. 4,089,029. Employed instead of the index hole in the disk is a permanent magnet or light reflector disposed in a preassigned angular position on a rotary part of the disk drive mechanism, such as the rotor of the disk drive motor of the rotor outside stator configuration. It is therefore essential that this rotary part of the disk drive mechanism be exactly in a prescribed angular relationship to the magnetic disk on the turntable. The variable degree of slanting of the drive pin impairs this angular relationship between the rotary part and the magnetic disk.